• PCV valves regulate air circulation in a crankcase.car engine image by itsallgood from Fotolia.com
  
  The Positive Crankcase Ventilation valve, or PCV valve, connects the crankcase to the intake manifold in order to regulate air flow. It is typically a small and inexpensive piece that is easy to change. Often it is recommended that when you change your spark plugs, you should change out the PCV valve as well, regardless of the vehicle. Prior to 1963, engines sent the crankcase exhaust into the atmosphere, an inefficiency corrected by the PCV system.
  
  

Functions

• Air is drawn from the crankcase to the intake manifold through a vacuum. This valve is instrumental in regulating the air/gasoline mixture as well as acting as a flame trap. It keeps the ventilation system clear of moisture according to Jakob Jelling of authorized.com by providing constant circulation.
  
  

How It Works

• The plunger in the PCV is drawn forward to restrict the flow of vapor. At low engine speeds, this pressure is highest according to burtonpower.com. As speed is increased, the vacuum drops and the plunger slides backward, increasing the amount of air allowed to flow through the system. These flow rates are different for each engine,
  
  

PCV Valve Failure

• If a PCV valve fails, excess pressure can cause gas vapors to back up into the air filter, or seals to break, leading to oil being sucked out of the engine. It can also cause improper air/gas mixtures, which will cause a rough idle. "The Environmental Protection Agency rules prohibit tampering with any emission control device," according to aa1car.com, which includes removing the PCV valve.
  
  

PCV Maintenance

• The most common problem with PCV valves is that they can get plugged up with engine sludge. Newer car manuals suggest replacing the PCV valve every 50,000 miles, but some older cars do not mention it. It is a small and inexpensive piece of equipment, and is very easy to replace. An easy way to check your PCV valve is to remove it from the engine and shake it. If you hear a rattle, then that means the plunger is loose and you need to replace it.
  
  

Replacing a PCV Valve

• Check your owner's manual to determine the location of your particular vehicle's PCV valve. You should not need any special tools, just disconnect the valve from the tubing and install the new valve. Be sure that the new valve is installed in the same direction as the old one.